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Components for medical applications

Components for medical applications Nigel Pritchett, managing director at Elesa UK, looks at the considerations for specifying components for postural seating and therapeutic equipment.

The specifications for components of postural seating and therapeutic equipment - such as chairs, wheel chairs, wheeled walker frames, massage couches, beds and support frames - have developed substantially in recent years along with the industry. This is perhaps especially true of those products designed to improve the quality of life for children with special needs.

Widespread requirements have been identified for seating of able bodied individuals to maintain good posture and good health as well as seating for people with special needs to aid greater comfort and stability. In these cases individual adjustment is essential to provide properly distributed support e.g. to feet, arms, buttocks, thighs, back/lumbar region and head. This often complex seating can require fully adjustable components frequently customised with additional items such as lateral supports. Similar needs were found in transport conversions, adjustable desking and tables for home or office working as well as adjustable beds and access equipment. Not only are these extremely functional mechanisms but they are also required to be aesthetically of a high standard.

At Elesa we have found that applications into this product group require standardised but specialised components for the locating and clamping of these adjustable assemblies. Specific categories of mechanism were identified:
  • Extensible tubes with clamping actions
  • Rotating joints with indexing positions
  • Rotating joints with continuous clamping adjustments
  • Temporary locating & clamping of equipment
  • Operating levers for actuating mechanisms

Consequently our engineers initiated a program of development that sought to accommodate the needs of this important industry.

Initially we found that typically the design of these types of adjustments can involve an inner tube sliding within an outer tube or sleeve. The inner tube which extends to achieve the required distance setting is invariably of a high surface finish for aesthetic reasons and may often be chrome plated for aesthetic or hygienic reasons.

We listened to Postural Seating Manufacturers who often commented on problems of achieving sufficient torque on clamping components to achieve the necessary clamping forces required to hold adjustments in place, specifically those that could experience a lot of weight such as foot plates and back rests. It also became evident after a period of use that the inner adjustment tubes were becoming scratched and damaged from the clamping systems then being used.

Invariably this was down to the use of poorly designed clamping products that were not of an ergonomic design and as such didn't allow sufficient torque to be applied - and in many cases this was further compounded by the incorporation of conventional bolts to form the clamping point as oppose to custom designed inserts.

Other factors found to be influencing design requirements were the need, in some cases for adjustment to be made by occupational therapists or under parental control and protected from misuse, or the ability to make adjustment when the grip of an operator may be impaired in some way.

All of these factors were taken into account by the Elesa technical department while understanding that cost would also be an issue when investigating suitable solutions. The specification mix defined a number of new products and variants derived from the Elesa range thus extending the lineage of quality, functionality and value previously established.

Elesa took its well proven VCT five lobe knob design which already incorporated purpose designed inserts with faced and chamfered ends and overmoulded a "soft-touch" thermoplastic elastomer to improve grip and aid torque. In instances where the end of the stud is clamping highly finished tube, further enhancements were enabled with the addition of delrin inserts in the end of the studs.

The standard range of VCT Clamping Handknobs represent a significant improvement over older style products manufactured in thermosetting material (which can shatter on impact) and in this case the glass reinforced thermoplastic construction not only confers high ruggedness and impact strength but is also ideal for the overmoulding process. A major additional feature of the VCT series is the availability of coloured centre caps which are available in blue, red, yellow, orange, grey and black (standard). These allow for colour coding of equipment functions or matching of finish to equipment for improved aesthetic appearance. For alternate functions female and through threaded versions are offered with brass inserts
while male versions have zinc plated steel studs. The VC range of 5 lobe grip knobs also offers the aesthetically striking chrome version - the VC.692-CR as a cost effective alternative to stainless steel which also addresses the hygiene issues involved in frequent use medical situations.

For applications requiring a level of protected adjustment the Elesa technical department introduced the VLS security knob, a further derivative of the VCT five lobe design incorporating a security key. VLS security lobe knobs (Elesa patent) have been designed to be unsecured only by authorised personnel provided with the ingenious security key. Without the key inserted the knob can be clamped in the conventional manner and with the key in place it unscrews as normal, but when the key is removed an internal ratchet mechanism operates with an audible click warning so the knob cannot be undone and the knob head simply ratchets around whilst the clamping action remains fixed; thus ensuring that important settings are not lost and that adjustments are not made by unskilled personnel.

Two types of key are available - a fold down type to be left in place, e.g. for use throughout the working day, and then removed; and a ball top key to be kept on a key ring for occasional use - both have red moulded handles for ready identification.

For ultra-quick clamping operation the Elesa range of eccentric cam operated levers is ideally suited to equipment mounting on tubular frameworks. The LAC series are designed for attachment to medical furniture, wheelchairs, trolleys, orthopaedic seating, therapeutic products, bicycles or other mobile equipment where rapid fixing/removal or re-positioning is required, e.g. rapid assembly of mobile stands or supports.

LAC cam-clamps feature a smooth action cam clamping plate arrangement with fine adjustment by means of a knurled knob, or as a non-adjustable configuration. This cam with plastic clamping plate design ensures smooth torque free clamping to eliminate movement or "wriggle" during the clamping process, as well as ensuring that the clamping force cannot exceed set limits, which can be as high as 5000N. Both adjustable and non-adjustable types are available in female or male formats and thread forms of M8.  Since the LAC clamps are intended for frequent manual operation, Elesa have paid special attention to ergonomic features such as touch comfort, feel and fit, using well proven glass-reinforced polyamide technopolymer for the hand lever itself.

For adjustments where high forces are involved Elesa recommends the use of indexing plungers to give a positive lock in a number of pre-determined positions as opposed to relying on the clamping force of a handknob. These are the kind of item vital in many situations, but often requiring space difficult to achieve and giving an awkward appearance if too large. Mini indexing plungers of the GN 822 series feature an AISI 303 stainless plunger which provides accurate positioning while the technopolymer knurled knob offers a safe and solid grip during operations. They are ideal for these applications due to their low overall height and shortened threaded body. Options are available with and without lock out "rest" positions.

In the Elesa technical department many other components are also coming under scrutiny for medically related applications - items such as handles, clamping handles, castors and even hand wheels come into this arena where increasingly special considerations are becoming the norm.

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